Direct-current voltage amplifier



Dec. 6, 1949 4 CARPENTER 2,4993??? DIRECT CURRENT VOLTAGE AMPLIFIERFiled Dec. 6, 1947 Patented Dec. 6, 1949 2,4905 27 DIRECT-CURRENTVOLTAGE AMPLIFIER Edmond Egbertus Carpentier, Eindhoven, Netherlands,assignor to Hartford National Bank and Trust Company, Hartford, Conn.,as trustee Application December 6, 1947, Serial No. 790,176 In theNetherlands, October 25, 1946 Section 1, Public Law 690, August 8, 1946Patent expires October 25, 1966 6 Claims. (Cl. 179-171) The inventionrelates to direct-current voltage amplifiers wherein the voltagerequired to be amplified is supplied to the input circuit of atube-amplifier by means of a mechanically operated quick-acting switch.

Direct-current voltage amplifiers without a mechanically operatedquick-acting switch exhibit the disadvantage that if the input voltageof the amplifier remains constant, a voltage which is variable with timeis set up in the output circuit, said action being referred to as driftof the amplifier. Steps are known per se for counteracting this drift ofthe amplifier.

In a direct-current voltage amplifier comprising a mechanically operatedquick-acting switch the voltage to be amplified and a constant voltage(for example, the voltage zero) are supplied successively to the inputcircuit of the amplifier. From the output circuit are taken two voltagesthe difierence between which is independent of the drift of theamplifier.

There remains, however, the drawback, that each of the two voltagestaken from the output circuit is dependent upon the drift of theamplifier. This drift may occur to such an extent that the absolutevalues of the voltages lie outside the measuring range of a measuringdevice responsive to these voltages, for example a cathode ray tube.

In order to eliminate this disadvantage, the invention provides a simplesolution in the device under consideration.

According to the invention, the mechanically operated quick-actingswitch is connected in such manner that in one position of this switchthe voltage to be amplified and, in the other position, a voltagederived from the output voltage of the amplifier with the aid of anetwork the time constant of which is preferably smaller than theswitching period of the quick-acting switch, is made operative in theinput circuit of the amplifier.

The invention will be explained more fully with reference to theaccompanying drawing in which:

Fig. 1 illustrates one form of an amplifier in accordance with theinvention, and

Fig. 2 illustrates a modification of the arrangement shown in Fig. 1.

In Fig. 1 the voltage to be amplified is supplied via terminals l and 2to a contact 30f a mechanically operated quick-acting periodic switch,for example a vibrator switch. The arm 4 of the switch is connected tothe control grid of a discharge tube 6 in the anode circuit of which isset up an amplified voltage which is supplied to deflector electrodes 1of a cathode ray tube 8.

A switch arm 5 is moved in synchronism with the switch arm 4 of themechanically operated quick-acting switch. In the position of theseswitch arms at which the grid of the discharge tube 6 acquires thevoltage of the contact terminal 2, part of the anode voltage of tube 5,which part is determined by resistances 9 and I0, is supplied by theswitch arm 5 to a condenser ll included in the grid circuit of tube 6.The time constant of the network 9, II], II is chosen so as to besmaller than the switching time of the quick-acting switch.Consequently, the condenser ll assumes a potential which is proportionalto the voltage across the electrodes at the time when the switch is inthe position with the arms 4' and 5 connected to the respective lowercontacts. At this time a negative feed -,back'voltage is applied to theinput circuit b,

the elements 9, l0 and H, thereby counteracting any variation of thesaid voltage of the electrode I and making the said voltage independentof the drift of the amplifier.

The time constant of the condenser H and the resistance It) is so largethat the condenser does not discharge to any significant extent duringthe period of time in which the switch occupies that position in whichthe grid of the tube 6 assumes the potential of the contact terminal I.Accordingly in this position of the switch the voltage set up in theanode circuit of tube 5 will likewise be independent of the drift of theamplifier so that the disadvantage inherent to the known device iseliminated. If the time constant of the network 9, ll], H were greaterthan the switching frequency of the quick-acting switch, there is thedanger that the control effected would not be sufficiently rapid.

It is advantageous to make the switching frequency of the quick-actingswitch as high as possible, for in this case it is possible toneutralize not only slow variations of the characteristics of theamplifying tube 6 but also those variations which are due, for example,to changes in line voltage and to hum.

The period of time during which the grid of tube 6 assumes the potentialof the contact terminal is in general chosen so as to be longer at leastby a factor 5 than that during which this grid assumes the potential ofthe contact terminal 2. In this case the time constant of the network 9,l0, II will be taken still smaller than has been mentioned above. Tothat end the resistance 9 may be replaced by a blocking condenser or theresistance [2 included in the cathode circuit may be given a highervalue.

In the arrangement shown in Fig. 2, the mechanically operated switchcomprises a single arm member which alternately connects thecondenser-resistor network l'I-Hl to'the terminal 2 of the source ofvoltage to be amplified and to the resistor 9 of the feed back path. Theterminal of the voltage to be amplified is fixedly connected to the gridof the amplifier tube.

The invention is not limited to' the example illustrated but may, ofcourse, also be applied to amplifiers comprising a plurality of tubesand'to push-pull or cathode coupled amplifiers. If desired, anamplifiying tube may be incorporated in the circuit of the resistance a.

What I claim is:

1. A direct-current voltage amplifier circuit arrangement comprising anelectron discharge tube having a cathode, a control grid and an anode;an input circuit for applying the voltage to be amplified to the cathodeand grid of said discharge-tube; an output circuit coupled to saidcathode and anode for producing an output voltage, mechanically actuatedswitching means for periodically interrupting said input circuit, andmeans to periodically apply said output voltage to-s'aid control grid innegative feedback relationship during the said interruption of saidinput circuit.

2. A direct-current voltage amplifier circuit arrangement comprising anelectron discharge tube having a cathode, a control grid and an anode,an input circuit for applying the voltage to be amplified to thecathode-and grid of said discharge tube, an output circuit coupled tosaid cathode and-anode for producing an output voltage, mechanicallyactuated switching means for periodically interrupting said inputcircuit, and means to periodically apply said output voltage to saidcontrol grid in negative feedback relationship during the saidinterruption of said input circuit, saidilatter means comprising anetwork having a chargingtime-constant shorter than the period of saidswitching means and a discharging time constant greater than the periodof said switching means.

3. A direct-current voltage amplifier circuit arrangement comprising anelectron discharge tube having a cathode, a control grid and an anode,an input circuit for applying the voltage'to be amplified-to thecathode'andgrid ofsaid'discharge tube, an output circuit coupled to saidcathode and anode for producing an output voltage, mechanically actuatedswitching means for periodically interrupting said input ci'rcuiigandmeans to periodicallyapply said output voltage to said. control grid innegative feedback relationship during the said interruption of saidinput circuit, said latter'means-comprising a first resistanceelementcoupled to said cathode and grid, a capacitance element shuntingsaid resistance element, a switchingelement operative: in synchronismwith said switchingmeans'and" coupled to said first-resistance element,and a second resistance element coupled between-said anode and saidswitchingelement.

i. A direct-current voltage amplifier circuit arrangement comprisinganelectron discharge: tube having a-cathode, acontrolgrid and'an-anode,an input circuit for applying the voltage to be amplified to the cathodeand grid of said dis-' charge tube, an output circuit coupled to: saidcathode and anode for producing an output voltage, mechanically actuatedswitching means for periodically interrupting said input circuit in aratio at which the voltage to be amplified is connected to said cathodeand grid for a time interval greater than about five times the period ofsaid interruption, and means to periodically apply said output voltageto said control grid in negative feed-back relationship during the saidinterruption of said input circuit, said latter means comprising afirstresistance element coupled to said cathode and grid, a capacitiveelement shunting said resistance element and forming therewith a networkhaving a time constant greater than said time interval, a switchingelementoperative'in synchronism with said switching means and coupled tosaid first resistance element, and a second resistance element coupledbetween said anode and said switching element and forming With saidcapacitive element a network having a time constant less than saidperiod of interruption.

5'.- A direct-current voltage amplifier circuit arrangement comprisingan electron dischargetubehavinga cathoda a control grid andan-anode,aninput circuit comprising a first conductor and a second conductorfor'applyng' the voltage tobe amplified to the cathode and grid of saiddischarge tube, an output circuit coupled to said cathode andanode forproducingan-outp'ut voltage, mechanically actuated'fir'st switchingmeans for periodically selectively connecting said first andsecondconductors to said grid comprising a switch arm member connected tosaidgrid; a

first contact memberconnected'to said first conductor and a secondcontact member connected to-said'second conductor, and means to'period--pled to said output circuit andsecondswitchingmeans: operative insynchronism with said'first switchin means to periodically connect saidsecondresistance element to said first resistance element.

6. A direct current voltageam'plifiercircuit arrangement comprising anelectrondischarge tube @having a cathode; a control grid andan anode,

an input circuit comprising a first conductor connected to said grid anda second conductor for applying the voltage to-be-amplified to-thecathode and grid of said discharge tube, an output circuit-coupled tosaidcathode-and anode for producing an output-voltage; mechanicallyactuated switching: means for periodic-ally interrupting saidinputcircuit comprising a switch arm member coupled to said cathodeand'a first contact member coupled to said second conductor, and meansto periodically apply said output voltage to said control grid innegative feedback relationship during the said interruption of saidinput circuit, said meansv comprising afirst re-- sistance elementinterposed between said switcharm member and said cathode, a capacitanceelement shunting; said first resistance-element,-a-

second contact member selectively engaging said switch arm memberduring-interruption of said input circuitand a second resistance elementcoupled between said output circuit and said second contact member.

EDMOND EGBERL'I-US CARPENTIER.

(References on following page) REFERENCES CITED The following referencesare of record in :the file of thie p atentr 1 UNITED STATES PA'I'ENTSNumber Name Date 1,820,212 Bauer Aug. 25, 1 931 Number

